Selective amplifying apparatus



M. l. PUPIN SELECTIVE MPLIFYING APPARATUS Original Filed oct. 1o, 1918 a 60 noma/to@ -MMML 1.71,

' character. More particularly, the invention' Patented pr. 1, 1924.

lUisurizo yfs,#ritira/.s PATENT oF FICE.

MICELAEL IDvoRsxYiPiiPIm-,CP NORFOLK, CONNECTICUT, AssIGNoR To WEsTING- noU'sE ELECTRIC AND'MANUEACTURING coMPANY, or EAsT PITTSBURGH, PENN- sYLvANIA, A CORPORATION or PENNSYLVANIA. v ,I

SELECTIVE .AAMPLIFYING APPARATUS.

Application led October 10,l 1918,` Serial No, 257,572. Renewed September 5, v1923.

T o'la'll whom it may concern.'

Be it known that I, MICHAEL I. PUPIN, "a citizen'of the United States, residing at 4 Norfolk, in, the county of Litchfield, State of Connecticut, have invented certain new 'and useful Improvements in Selective Am- Vplifying Apparatus; and I do hereby declare the following to be a full, clear, and 'exact description Vof the invention, such'as Twill enable others skilled in the art to which it a pertains" to make and use the same. vIfliis'inventionrelates. to kselective amplifying apparatus -for electric energy waves, and has for its general object vthe provision of an improved-"apparatus of th1s l relates to apparatus including a transformer having large dissipative reactions, and in this connection the aim of the 1nvention is the provision of means for d1- minishing these reactions. Other objects of the invention will be brought out in t-he course of the following description.

In an apv lication filed concurrently herewith, Seria No. 257,570, I have described a wave balance having a wave conductor with substantially uniformly distributed inductance, resistance and capacity and secondary coils or circuits inductively related thereto and relatively movable with respect 'to each other and to the conductor. And in 'another application filed concurrently herewith, Serial #257,571, I have described a selective amplifying apparatus embodying such a ,wave balance for the purpose o f securing the desired selectivity and in which the'amplifying excitation is increased by the action of the wave balance.

The present invention contemplates the Iuse ofthe wave balance .for diminishing the dissipative reactions,` and in particular l the effective resistance of the primary cir'- monic electromotive forces.

cuit, of' a selective electromagnetic transformer suitable for high frequency har- This aspect of the invention, in its preferred form', in-

f volves the provision of a wave balance whose wave conductor is energized by` the pulsatingclectromotive force of a vacuum tube empliier whosey grid is excited by the secondary 'winding of the transformer. These and other arrangements contemplated by the invention 'will be better-understood ,from the following, description takenV in conjunction with the accompanying drawpart of this specifica-tion,

of a selective amplifying apparatus embody-` ingthe principles of the invention; and

Fig. 4 illustrates ,two characteristic curves which will be explained hereinafter.

The construction of a transformer, suitable for purposes of this invention, will be explained in connection with some definite practical conditions under which it is to operate. It is assumed in this specification that the V primary winding of the transformer is to be connected to the plates of a quartz oscillator comprising a quartz crystal lia-ving metallic electrodes orconducting plates operatively arranged on the surface of the crystal, such as is now employed in submarine signalling by sound waves, having a frequency yabove the limit of audition, and the frequency of these waves is assumed to be 50,000 P. P. S. It is to be understood, however, that these assumptions are made merely for explanatory purposes, and that the invention is lnot limited to this particular embodiment. The electrical capacity of the oscillator is assumed to be 10' farads. The primary winding of the transformer is connected in series with the oscillator.v In order that the inductance-reaction of the primary winding neutralize the capacity reaction of the oscillator, for 50,000 P. P. S., the effective primary inductance should be approximately '102 henrys when the primary is in actual operation. This fixes the lower limit of the secondary turns for a given ratio of transformation. It is assumed here that the ratio of turns is about 6, thatis, the secondary Winding must have approximately six times as many turns as the primary winding. It will be seen that y diagrammatic view illustrating uniformly distributed inductance, resistp ance and capacity for frequencies of the order of 50,000 P. P. S., and will develop in the primary a large elfective resistance even when the secondary circuit is openor conactance, then the ratio of transformation of the impressed electromotive force is not equal to the ratio of turns, but much less;

that is to say, the transformer becomes inef-I fective. A particular object of thisv invention is to remedy this defect by diminishing the eective resistance of the primary at the ex' Y pense of electrical energy supplied to the primary from an independent source. To this end, the invention contemplates, in its preferred form, the provision of a selective electromagnetic transformer I suitable for high frequency harmonic .selectro'motive forces in which the eective resistance of the primary circuit is compensated selectively by a negative resistance reaction produced in the primary circuit by the action of a wave balance energized by the pulsating elec- ,tromotive force of a vacuum tube amplier whose grid is excited by the secondary of the transformer.

Referring now to Fig. 1 of the drawings, there is diagrammatically represented a transformer having a magnetic core made up of an outer rectangular member 5 and 100 an inner member 6. The'inner core mem-V ber 6 forms the central leg ofthe magnetic circuit, while the outer core member 5 serves to supply a low reluctance vpath for the central core. The rima winding 7, and the v secondary winding 8 o the transformer, are

wound and mounted on the leg 6 of the core.

It is preferable to separate the two transvy former windings as much as practicable, as

indicated invFlg. 1, andtlius reduce their mutual capacity.

The arrangement of the secondary winding 8 is indicated in Fig. 2of the drawings.

`The secondary winding,'as represented in this figure, consists of five layers of wire,

with the consecutive layers spaced a art by `insulating distance piecesl 9 arrange in the corners. The largest part of the lnsulation between the layers of the secondary winding is air insulation. By separatin these lay' ers as much as practicable and y employing air insulation the capacity of 'the sec- 'ondarvwinding is muchy reduced, which is l,

desirable.I 1 This method of winding will-be f referred to as `the Morecroft -wnd1ng',-"af

v125..ter 'Professor Morecroft who developed-it.

I will now describe the specific construcvtion of a transformer which I have success- .fllyoperated lThe magnetic core of this transformer'ismade 'up' of plates ofcold 130.1'olled sheet steel of approximately .007 c.`m.

-milll1enrys at. 50,000 P. P." S., its windin "ing.

vthe inductance to t e 'common' ground ter.

thickness. 350 plates are pasted together by y thin shellac, out of .which alcohol is expelled by careful heatingafter the core is madesyup and clamped. The external dimensions of the plates are 8 c..m. X 6 c.- m. The-.secondary winding consists of ve layers of #39 calido wire of ,high resistance, 1.6 ohms per c. m. The primary winding has 200 turns which giveit an inductance of .025 henrys when the secondary Winding is not present. 75 Its resistance is 600 ohms'at 50,000 P.`v PLS. most of which is due to"4 vFou'cault current losses in the iron core. -When, however,the secondary is placed upon the'core, 'as indicated in Fig. 1,' and the common terminal" of the primary and secondary windings is connected to ground, as indicated atl 23,fthen the effective resistance at 50,000' P. P. S.' is about 5,000 ohms and the inductance is greatly reduced.l This very considerable increase in the elfective primary resistance is due to the capacity current in the secondary, and the ratio of transformation is not' 6, which is the ratio of turns, but considerably less.

Referring now to Fig. 3 of the drawings, there is diagrammat'ically representeda low impedance vacuum tube amplifier, having a grid 10, a heatin filament 11 and a plate 12. A local source o direct current energy, such for example, as the batter 13, serves to supply the relatively low vo tage, say about 7 volts, for the filament 11, and the rela-v tively high voltage, say about 110. volts, for the wing or electron current between thev1 vfilament 11 and the plate 12. The late 12 is connected to the positive termina 'of' the coil 20, having an inductance of about'f40 40 and magnetic circuit bein so constructe as to avoid capacityas muc as practicable.

The grid 10 of the vacuum tube is connected to the ungroundedfterminal of the secondary'windin Sand is accordingly excited by an electrlcal reaction of this wind- A quartz oscillator 25, aresistance load 14, of aboutv16,000 ohms,\and a variable 'inductance 26 are included in seriesivith the primary winding 7 of 'the transformer. "50 The variable inductance 26 hel s to reduce the capacity reaction'of the oscillator. The primary circuit is roundedvby connecting minal`23. Y, :55

`Included in series relation `with the pri- 1 mary lcircuitv of the transformer are the two secondaryocoils 15 and'16' of a wave balance ofthe formdescribed inmy 'aforementioned 'appllcatlo'ns- This wave/balance comprises f 60 inner and youter 'laminated layersv of tin. foil "18 and 18 betweenwhich kis/positioned the coiled wave conductor 17, separated bysuitable` dielectric layers fromvv each tn`foil layer. The` wave conductor has substan- 65 tially uniformly distributed inductance and capacity and possesses suciently high resistance and capacity to make it a true wave conductor and to render it practically aperiodic. The secondary` coils and 16,

are inductively associated with the wave conductor 17 and are relatively movable with respect to each other and to the wave conductor.

Oneterminal of the wave conductor 17 is connected to plate 12 through a blocking condenser 21 designed to prevent the direct current voltage of battery 13 from establish- Y ing a direct current through the wave conductor. The blocking condenser should have a low reactance for the signalling frequency, say equal to 1150i the terminal impedance of the Wave balance. The common ground for all the conductors in the system is effected through the connection 23. f f

If the wave balance be removed from the apparatus and the oscillator 25 be connected directly to the primary winding 7 of the transformer, then the effective resistance and inductance of the P. P. S. will be over 10,000 ohms. But when the wave balance is connected in the apparatus as indicated in Fig. 3, then, by'suitable adjustment of the secondary coils 15 and 16, both as regards their position and the nume ber of turns in each, the primary effective resistance can be reduced to any limit. The

primary effective resistance can even be l made' negative, in which case the primary current will oscillate even without an impressed electromotive force, the period of oscillation being determined by the capacity of the oscillator 25 and the effective inductance of the primary circuit for the frequency of the oscillation. The occurrence of these oscillations isfthe disturbing element in the arrangement of circuits just described, and the provision of vmeans for preventing their occurrence is an important element of this invention. l

An examination of the disposition of the circuits in Fig. 3 shows that it is similar to.

that employed in some heterodyne oscillators. But there is this distinction; in.. the arrangement of Fig. 3, the secondary winding 8 acts like a wave conductor withfunil formly distributed resistance, inductance 'and capacity, and will have a large number of natural periods of its own. uThisjs not the case in ordinary heterodyne oscillators.

To prevent the system froml oscillatin i in.

accordance with one of these natural periods is difiicult when the oscillating' system is coupled to the. plate circuit of a vacuum tube amplifier, aslndicated in Fig. 3. The arrangement which this invention provides for suppressing these natural oscillations consists in making the resistance of-the secondary winding sufliciently large, and for this purpose the secondary'winding l8 is primary for 50,000 y wound with #39 calido high resistance wire, having a resistance of about 1.6 ohms per c. in. so that the total resistance of Vthe secondary Winding 8 is about 22,000 ohms. To provide a mathematical formula which` will predetermine theoretically the amount of resistance which must be put into the secondary circuit under any given conditions that may arise in such a system as represented in Fig. 3, is next to impossible.

It is clear, however, that' a given diminu-` tion of the effective resistance in the primary circuit of the transformer requires a definite amount of energy-to be supplied by the' generator orvsource of power which operates the vacuum tube. SomeV of this energy is transferred to the secondary circuit of the transformer and if this energy is smallerv than the heat developed in the secondary circuit by the partial natural oscillations thereof, then these oscillations cannot be sustained. The practical rule is: To make the coupling between the primary circuit yandthe wave balance sufficiently strong to the success of this impirical method of operation is the stability of thestructure as indicated by. the absence of free oscillations in the secondary circuit.

A very substantial increase in the stability ofthe structure or system 'is obtained by inserting in the primary circuit of the transformer an extra resistance of large value, say 16,000 ohms, which Vis represented in Fig. 3 by the numeral I4, and thenconnecting the secondary coils 15 and 16 of the wave balance by the so-called inverse series connection` and displacing the secondary coilsby adistance which is approximately equal lto one-half ofthe wave length for the frequency which is to be transmitted. As explained in my aforementioned application Serial #257,571, filed October 10, 1918, the primary `circuit then becomes selective, excluding both the lower and the higher frequencies. The-Jefective resistance afterreductionshould be sufiiciently high to give 4vthe primary circuit so small a time constant as to makeit practically aperiodic. This can always be Vdone by sacricing a certain amount of selectivity. o y

The selectivity ofthe structure or system diagrammaticallyrepresented in Fig. 3 is illustrated by the curves of Fig. 4. In Fig. 4, the curve designated A, the data for which were obtained experimentally, expresses the llli '- uuitn tube (the. pulsating relation between the impedance of the primary circuit of the transformer and the frequency of the impressed electro-motive force. -The abscissee of this curve denote the frequency in kilo-cycles, and the ordinates denote the corresponding impedance in thousand of ohms. The curve of Fig. 4.- designated B, also experimentally obtained, illustrates 4the selectivity by studying the amplifying lpower of the vacuum tube at the same frequencies and under the same conditions under which curve A was obtained. Curve B expresses the relation between the frequency of the electro-motive force impressed upon the primary circuit and the amplifying power of the vacuum tube and its conductors as represented in Fig. 3. The abscissae of curve B represent the frequency in kilo-cycles, and the ordinates represent the amplifying power, that is, the ratio between the potential of the pulsating electro-motive force of the vacplate 12), and the potentialor the electromotive force impressed upon the rimary circuit. The experimental determinations from which curve B was obtained was conducted by means of a wave balance as described in my aforementioned application- Serial #257 ,570, filed October 10, 1918.

It should be observed that the vacuum tube 'employed here is a power tube, that is, a

low impedance vacuum tube which is capable of supplingx a relatively large amount of power. ig impedance vacuum tubes cannot do this, and hence are not as suitable for the operations described herein. The characteristic element in these operations is to yload the circuits with resistance reac-v tions and then rely upon the power tube to carry this load selectively, and the result 1 is not only selectivity, but also large amplification which power tubes cannot do under ordinary conditions, because, as ordinarily employed for amplifying purposes, the Vpower tubes are not given a suiciently good opportunity to do work.

It is to be understood that the structure represented in Fig. 3 is a selective sin le step amplifien'and thatas such it can e employed in the construction of a multistep selective amplifier. This practical application 4of the structure is discussed in my aforementioned application ISer. No. 257,571, and is not claimed herein, the resent a plication being more particu arly limite to the provision, ina supersonic signalling system, ofy a suitable selective transformer circuit for the receiving oscillator of the condenser type which will connect the oscillator to the translating device, as described in the aforementioned application Serial #257, 571.

I claim:

1. In an apparatus of the character .de-

from said source.

voltage of the amplifier excited by an electrical reaction of the secondary winding of said transformer,

a source of electric energy, and means for placing the primary circuit of said trans-Y former in inductive relation with the electron circuit of the vacuum tube and for conveying power to said primary circuit 2. In an apparatus of the character described, an electromagnetic transformer with large resistance reactions, a source of electric energy, and means for compensating the resistance reactions of the transformer by supplying electrical energyfrom said source to the transformer circuit. y

3. A selective amplifying apparatus comprising an electromagnetic transformer having large resistance reactions, a control device, and a` negative resistance compensator controlled'by said device and arranged` to impress a negative resistance reaction on a circuit including a' winding of said trans` former.`

4. A selective amplifying apparatus com- .prising an electromagnetic transformer having large dissipative reactions, acontrol device, a source of electric energy and a wave balance arranged'to transfer byinduction and under the control of said device electric wave energy from said source yto a circuitl 'including a winding of said transformer.

\ 5. A selective amplifying apparatus comprising an electromagnetic transformer 'having large dissipative reactions, a vacuuml tube,a source o electric energy, and awave balance arranged to transfer byinduction and under the control of said' vacuum tube electric wave energy from said source to a' circuit .including awinding of` said transformer.

6. A selective amplying apparatus comrising an electromagnetic transformer having large dissi ative reactions, .an amplify-` ing device excited byan electrical reaction of said transformer, and a wave balance controlled by said device and having secondary circuits in inverse series connection'arranged to impress a negative resistance reaction upon acircuit including a windngof said transformer.

7. A selective amplifying apparatus comrising an electromagnetic transformer having lar e dissipative reactions, avacuum tube excited by an electrical reaction of said transformer, 'a source o f electric energy, and a wave balance having secondary circuits in inverse series connection and arranged so that its energizing current is controlled by the pulsating electromotive force of .said tube for the purpose of conveying ower from said source to a circuit inclu g a winding of said transformer.

8. A selective amplifying lapparatus comsecondary winding of said transformer, a

source of electric energy, and a wave balance havin a wave conductor energized by a pulsating H electromotive force controlled by said tube and having secondary coils in inverse series connection included in the primary circuit of said transformer and arranged to impress upon said primary circuit a negative resistance reaction whose energy is lderived from said source.

9. A selective amplifyingapparatus comprising an electromagnetic transformer hav- 1ng large resistance reactions, a vacuum tube excited by an electrical reaction of the secondary winding of said transformer, a source of electric energy, and a negative resistance compensator which by conveying power from said source to the primary circuit of said transformer increases the exciting reaction of said. secondary winding.

10. A selective amplifying apparatus comprising an electromagnetic transformer having large resistance reactions, an amplifying device excited by an electrical reaction of the secondary winding of said transformer, a source of electric energy, and a negative resistance compensator which by conveying power to the primary circuit of said transformer from said source increases the exciting reaction of said secondary winding.

11. A selective amplifying apparatus comrising an electromagnetic transformer having large resistance reactions, an amplifying device excited by an electrical reaction of said transformer, a source of electric energy,

and a negative resistance compensator which by conveying power from saidsource to a circuit including one of' said transformer' windings increases the exciting reaction of the transformer.

12. In an apparatus'of the character described, an electromagnetic transformer having large resistance reactions, a source of electric energy, and a negative resistance compensator electrically associated with said 'transformer forl diminishing the effective resistance of, the primary circuit of the transformer by supplying electric energy thereto from said source. 1

13. In' an apparatus of the character de- `scribed, an electromagnetic transformer having large dissipative reactions, a lsource `of electric energy, and aV wave .balance ar-" ranged to transfer by induction electric energy from said source to a winding ofl said transformer.

14. In an apparatus of the character described, an electromagnetic transformer having large dissipative reactions, a source of electric energy, and a wave balance having secondary coils in inverse series connection electrically associated with (the primary circuit of said transformer for diminishing the effective resistance of said circuit at the expense of electricall energy supplied thereto from said source.

15.Y The combination with an electromagnetic transformer and a source of electric energy, of a wave balance ,arranged to transfer by induction electric energy from said source to a winding of said transformer for diminishingthe effective resistance of the primary circuit of the transformer.

16. A selective amplifying apparatus comprising an electromagnetictransformer havmg large Adissipative reactions, a vacuum tube'excited by an electricalreaetion of said sav substantially. uniformly distributed inductance, resistance and capacity, a vacuum tube excited by an electrical reaction of said secondary winding, a sourcev of electric en. ergy, and a wave balance having a wave conductor whose energizing current is controlled by the pulsating electromotive force` of said tube and having secondary coils in inverse series connection included l in the primary circuit of said transformer and arranged to diminish the effective resistance of said primary circuit byv impressing thereon a negative resistance reaction whose cn-` ergy is derived from said source. A y

In testimony whereof I alix my signature. MICHAEL IDVORSKY BUPIN.

ico 

